1. Field of the Invention
The present invention relates to an external combustion engine using evaporation and condensation of a working medium to displace a liquid part of the working medium and converting the displacement of the liquid part of the working medium to mechanical energy for output.
2. Description of the Related Art
In the past, this type of external combustion engine is also called a “liquid piston steam engine” and is configured sealing a working medium in a tubular container in the liquid phase state, using an evaporator formed at one end of the container to heat and evaporate part of the liquid phase state working medium, using a condenser formed at the middle of the container to cool the vapor of the working medium to condense it, using this evaporation and condensation of the working medium to cyclically displace a liquid part of the working medium (so-called “self vibration”), and taking out the cyclical displacement of the liquid part of this working medium at the output part as mechanical energy (for example, Japanese Patent Publication (A) No. 2004-84523).
This Japanese Patent Publication (A) No. 2004-84523 describes a so-called “single-cylinder type” liquid piston steam engine where the container as a whole is formed into a single tubular shape.
On the other hand, Japanese Patent Publication (A) No. 2005-330885 describes a so-called “multiple cylinder type” liquid piston steam engine configuring the part of the container from the evaporator to the condenser by a plurality of branched tubes and configuring the remaining part of the container (part at output part side) by a single header tube.
According to the prior art of this Japanese Patent Publication (A) No. 2005-330885, each of the plurality of branched tubes is formed with an evaporator and condenser, so the heat conduction areas of the evaporators and condensers increase. For this reason, the heating performance (evaporation performance) and cooling performance (condensation performance) of the working medium are improved, so the external combustion engine is improved in output.
Note that in the prior art of this Japanese Patent Publication (A) No. 2005-330885, the plurality of evaporators formed at the plurality of branched tubes are arranged in the flow of high temperature gas and use the high temperature gas as a heat source to heat the working medium.
Further, in the prior art of this Japanese Patent Publication (A) No. 2005-330885, a large number of branched tubes are arranged in two perpendicularly intersecting directions so as to reduce the size of the container compared to arranging a large number of branched tubes in just one direction.
In this regard, Japanese Patent Application No. 2006-78802 (hereinafter referred to as the “prior application example”) proposes a single cylinder type liquid piston steam engine improving the output and efficiency.
In this prior application example, when the peak value of the internal pressure of the container is lower than the saturated vapor pressure of the working medium at the temperature of the evaporator and becomes a value as close as possible to the saturated vapor pressure (hereinafter referred to as the “ideal peak value”), the external combustion engine becomes highest in output and efficiency (see later explained FIG. 2(a)). Considering this, the peak value of the internal pressure of the container can be adjusted by the pressure adjusting means in the container.
Further, if the temperature of the evaporator fluctuates and the saturated vapor pressure of the working medium fluctuates, the pressure adjusting means in the container adjusts the internal pressure of the container in accordance with this and makes the peak value of the internal pressure of the container approach the ideal peak value, so the output and efficiency of the single cylinder type liquid piston steam engine can be maintained high.
Note that the above prior application example describes, as one example of the pressure adjusting means in the container, an auxiliary container type controlling the internal pressure of an auxiliary container separate from the main container in which the working medium is sealed so as to adjust the peak value of the internal pressure of the main container.
More specifically, a working medium is sealed in a liquid state in an auxiliary container communicated with the main container and the working medium in the auxiliary container is compressed or expanded by a piston mechanism, whereby the internal pressure of the auxiliary container is controlled and as a result the peak value of the internal pressure of the main container is adjusted.
Therefore, the inventors studied the multiple cylinder type liquid piston steam engine described in the above Japanese Patent Publication (A) No. 2005-330885 so as to try to improve the output and efficiency using a pressure adjusting means in the container in the same way as the above prior application example.
However, the multiple cylinder type liquid piston steam engine of the above Japanese Patent Publication (A) No. 2005-330885 has the plurality of evaporators arranged in the flow of the high temperature gas, so the more to the upstream side of the high temperature gas the evaporator, the higher the temperature of the evaporator and the more to the downstream side of the high temperature gas the evaporator, the lower the temperature of the evaporator.
For this reason, if deeming the saturated vapor pressure at the temperature of the evaporator at the upstream side of the high temperature gas to be the ideal peak value and adjusting the peak value of the internal pressure of the container, the peak value of the internal pressure of the container will end up exceeding the saturated vapor pressure at the evaporator at the downstream side of the high temperature gas.
As a result, part of the vapor of the working medium ends up condensing at the evaporator at the downstream side of the high temperature gas and minus work ends up being performed, so there is the problem that the output and efficiency end up dropping (see later mentioned FIG. 2(c)) and in turn the output and efficiency end up becoming unstable.
In particular, in a system employing the above-mentioned auxiliary container type structure as the pressure adjusting means in the container, the evaporator at the downstream side of the high temperature gas is supplied with too much liquid phase state working medium and the amount of heat exchange at the evaporator ends up increasing, so the temperature of the evaporator ends up dropping. In the worst case, as a result of the temperature of the evaporator dropping, there is the problem that the self vibration of the working medium stops and the output can no longer be obtained.
Note that the inventors studied having a plurality of containers share a single pressure adjusting means in a container for the purpose of lightening the weight and reducing the cost, that is, using a single pressure adjusting means in a container to adjust the peak value of the internal pressure of the plurality of containers, but learned that problems similar to the above occurred when the temperatures of evaporators of a plurality of containers differ from each other.